Lists all PTY sessions (active and exited).

Use this tool to:
- See all running and exited PTY sessions
- Get session IDs for use with other pty_* tools
- Check the status and output line count of each session
- Monitor which processes are still running

Returns for each session:
- `id`: Unique identifier for use with other tools
- `title`: Human-readable name
- `command`: The command that was executed
- `status`: Current status (running, exited, killed)
- `exitCode`: Exit code (if exited/killed)
- `pid`: Process ID
- `lineCount`: Number of lines in the output buffer
- `createdAt`: When the session was created

Tips:
- Use the session ID with pty_read, pty_write, or pty_kill
- Sessions remain in the list after exit until explicitly cleaned up with pty_kill
- This allows you to compare output from multiple sessions
